The graphic billboards feature lumps of gristle, bones and connective tissue, claiming they are "common ingredients" in fast food.

The BHF hopes to make children think about what they eat and encourage them to make healthier diet choices. Director General Peter Hollins said: "Our research sends a shiver down my spine. Kids no longer know what they are eating. We must help them understand why some foods are healthier than others."

The BHF predicts half a million children will be diagnosed as overweight or obese within two years.

It wants a ban on fast food and fizzy drink advertising which targets them and the return of domestic science to the school timetable.